Types of scheme of supplying fuel from a fuel tank to an intake system of an internal combustion engine include a scheme of supplying fuel by using a fuel pump and a scheme of supplying fuel by using the gravity. According to the scheme of supplying fuel using the gravity, a fuel tank is disposed above a carburetor and the fuel is supplied from the fuel tank to the carburetor. Therefore, this scheme is often used because the configuration therefor is relatively simple.
In the case of the scheme of supplying fuel using the gravity, an automatic cock is disposed in a fuel supply path to supply the fuel from the fuel tank to the carburetor. The automatic cock is a valve that opens the fuel supply path using a negative pressure in a crankcase. During the operation of an internal combustion engine, a negative pressure is generated in the crankcase associated with a reciprocating motion of a piston (more correctly, a high negative pressure and a micro positive pressure are alternately and repeatedly generated). The automatic cock is opened by this negative pressure and the fuel in the fuel tank flows into the carburetor through the fuel supply path.
A common internal combustion engine rakes up a lubricating oil stored in the crankcase upward to splash the lubricating oil and, thereby, generates oil mist to lubricate a portion to be slid that is accommodated in the crankcase. This is not preferable because the oil mist adheres to parts in the automatic cock when the oil mist intrudes into the automatic cock.
In contrast, a fuel supplying apparatus is known as is disclosed in, for example, Japanese Patent Publication No. 4310294, that is adapted to suppress the intrusion of the oil mist into a negative pressure introducing inlet of the automatic cock. The fuel supplying apparatus is configured to connect a crankcase to an intake system through a gas/liquid separating apparatus, a breather path, and a reed valve and to connect a branch outlet that branches from the breather path to the negative pressure introducing inlet of the automatic cock.
When a positive pressure is generated in the crankcase, the reed valve is opened by the positive pressure. Oil mist and blowby gas produced in the crankcase are caused to circulate from the crankcase into the intake system and, thereby, are combusted in a combustion chamber. On the other hand, when a negative pressure is generated in the crankcase, the automatic cock is opened by this negative pressure. The fuel in the fuel tank is supplied to the carburetor through the fuel supply path.
The gas/liquid separating apparatus is positioned between the crankcase and the breather path, and separates the oil mist produced in the crankcase from the air. Therefore, the intrusion is suppressed of the oil mist into the negative pressure introducing inlet of the automatic cock through the breather path. In addition, the automatic cock is positioned immediately and exactly above the crankcase. Therefore, even if the oil mist starts to intrude into the negative pressure introducing inlet of the automatic cock, the oil mist tends to flow out into the breather path thereunder due to the gravity.
When the automatic cock is disposed immediately and exactly above the crankcase being adjacent thereto, the thermal influence needs to be fully taken into consideration that is caused by the heat dissipation of the internal combustion engine. When the automatic cock is disposed above the crankcase far away therefrom to avoid receiving the thermal influence, the degree of freedom of disposing the fuel supplying apparatus is reduced and, therefore, this is not preferable. In addition, the fuel supplying apparatus employs the scheme of supplying the fuel by using the gravity and, therefore, the fuel tank is positioned above the automatic cock. Especially, for a configuration that has an internal combustion engine and a fuel supplying apparatus incorporated as one unit such as, for example, a small sound-proof engine-driven generator, the height of the unit as a whole is often limited. To suppress the total height, it is considered to make the fuel tank thin. However, this result in reducing the capacity of the fuel tank and, therefore, this is not an advisable solution.
An improvement as below can be considered. During the operation of the internal combustion engine, the negative pressure in the crankcase is higher than the negative pressure in the air cleaner and, therefore, the difference between the negative pressures is usable. The improvement is as follows: the negative pressure introducing inlet of the automatic cock is connected to the crankcase using a first hose; a second hose is caused to branch from the first hose at a halfway point thereof; and the first hose and the air cleaner is caused to communicate with each other by the second hose. An airflow resistance increasing unit is disposed in the second hose to set the airflow resistance of the second hose to be higher than the airflow resistance of the first hose. The air in the air cleaner flows from the second hose into the crankcase through the first hose and, therefore, suppresses the intrusion of the oil mist in the crankcase into the negative pressure introducing inlet of the automatic cock to avoid the intrusion.
However, when the second hose is detached from the air cleaner or the first hose or when the second hose is broken, the external air receives an intake resistance due to the airflow resistance increasing unit and, therefore, is difficult to be sucked into the first hose. The negative pressure state of the first hose does not substantially vary and, therefore, the automatic cock maintains its opened state and the internal combustion engine maintains its operating state. Dust included in the external air may intrude from the first hose into the crankcase of the internal combustion engine. Because the internal combustion engine is in its operating state, the dust included in the external air may intrude into the combustion chamber of the internal combustion engine through the air cleaner. This phenomenon is disadvantageous for improving the durability of the internal combustion engine.